UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  2,  No.  7,  pp.  217-242,  plates  42-43,  3  figures  in  text  June  8,  1923 


INHERITANCE  OF  SOME  MORPHOLOGICAL 
CHARACTERS  IN  CREPIS  CAPILLARIS* 

BY 

VENKATA  KAU 


CONTENTS 

PAGE 

Introduction 217 

Objects  and  aims 218 

Material  and  methods 219 

Inheritance  of  length  of  leaf 221 

Inheritance  of  number  of  lobes  per  leaf 223 

Inheritance  of  size  of  capitulum 227 

Influence  of  age  of  plant 228 

Position  of  capitulum  upon  the  plant  as  a  factor 229 

Environmental  factors 230 

A  cross  involving  difference  in  head  size 232 

Discussion  of  results 233 

Summar}'  and  conclusions 236 

Literature  cited 237 


INTRODUCTION 

Geneticists  studying  the  inheritance  of  characters  in  plants  have 
been  following  with  interest  the  monumental  investigations  on  Droso- 
phila  by  Morgai)  and  others,  with  especial  attention  to  their  studies 
on  the  inheritance  of  both  qualitative  and  quantitative  characters. 
The  present  paper  reports  the  result  of  an  investigation  on  the  inheri- 
tance of  some  quantitative  characters  in  a  wild  plant,  Crepis  capillaris 
(L)  Wallr.  The  studies  included  characters  in  leaves  and  flowers, 
and  it  will  be  shown  that  the  inheritance  of  these  characters  is  similar 
to  the  inheritance  of  quantitative  characters  in  other  organisms. 

*Submitted  in  partial  fulfillment  of  the  requirements  for  the  degree  of  Doctor 
of  Philosophy  at  the  University  of  California. 


218  University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 


OBJECTS  AND  AIMS 

The  genus  Crepis,  comprising  over  150  species,  belongs  to  the 
tribe  Cichorieae  of  the  natural  order  Compositae,  and  is  closely  related 
to  the  genus  Hieracium.  The  species,  C.  capillaris,  so  far  as  known, 
has  not  been  brought  under  cultivation,  but  grows  as  a  wild  plant 
in  widely  separated  parts  of  the  world.  This  species  can  be  easily 
propagated  and  the  plants  are  self-fertile  so  that  investigations  may 
be  carried  on  with  inbred  strains.  Furthermore,  the  F1  and  P2 
generations  from  varietal  crosses  are  fertile  when  crossed  inter  se, 
and  the  species  has  a  very  low  number  of  chromosomes.  Hence  as 
Babcock  (1920)  pointed  out,  the  advantages  of  the  genus  for  genetic 
investigation  are  many.  Previous  to  that,  some  work  had  been  done 
on  the  cytological  side,  notably  by  Rosenberg  (1909-1918),  who  de- 
termined the  number  of  chromosomes,  Beer  (1912),  Miss  Digby  (1914) 
and  de  Smet  (1914).  De  Smet  has  given  excellent  illustrations  of  the 
various  stages  of  nuclear  division.  Other  species  of  Crepis  have  been 
studied  by  Rosenberg  (1909-1918)  and  Juel  (1905)  ;  interspecific 
crosses  between  C.  capillaris  and  C.  tectorum  have  been  reported  by 
Babcock  and  Collins  (1920).  The  achenes  of  C.  capillaris  germinate 
easily  after  a  short  period  of  rest  and  a  very  large  percentage  is 
viable.  The  plant  first  develops  a  rosette  and  finally  the  central  axis 
elongates  and  terminates  in  an  inflorescence;  but  under  unfavorable 
conditions  it  may  remain  indefinitely  in  the  rosette  stage.  The  plant 
is  strictly  annual,  however,  and  dies  after  once  flowering.  Plate  43 
illustrates  typical  plants  when  the  inflorescence  has  developed  and 
growth  has  practically  ended. 

The  present  investigation  has  to  do  specifically  with  differences  in 
the  length  of  the  radical  leaves,  in  the  number  of  lobes  on  the  radical 
leaves,  and  in  the  diameter  of  the  flower  heads.  The  aim  was  to  deter- 
mine whether  these  differences  were  inherited  and  to  locate  the  factors 
responsible  for  the  genetic  variations  as  distinct  from  modifications 
due  to  the  environment.  In  the  case  of  the  inheritance  of  morphologi- 
cal characters  in  the  leaf,  the  action  of  the  environment  had  to  be 
taken  into  consideration,  and  in  the  case  of  the  flowers,  the  action  of 
the  environment  in  addition  to  the  age  of  the  plant  and  the  position 
of  the  capitulum  upon  the  plant  had  to  be  evaluated  before  the  true 
genetic  variations  could  be  determined.    The  work  has  been  carried  on 


1923]  Eau:  Morphological  Characters  in  Crepis  Capillaris  219 

partly  in  the  greenhouse  and  partly  in  the  field  and  the  results  have 
been  found  so  consistent  that  the  data  have  been  combined.  The 
investigations  herein  reported  were  started  in  the  fall  of  1920  and 
were  carried  on  by  the  writer  until  July,  1922,  but  a  great  deal  of 
preliminary  purification  of  material  had  been  done  before  the  material 
was  turned  over  to  me. 

The  work  was  undertaken  at  the  suggestion  of  Professor  E.  B. 
Babcock,  head  of  the  Division  of  Genetics,  University  of  California, 
to  whom  my  best  thanks  are  due.  My  thanks  are  also  due  to  Dr.  K.  E. 
Clausen  and  Mr.  J.  L.  Collins,  of  the  Division  of  Genetics,  for  espe- 
cially valuable  help  and  suggestions  during  the  progress  of  the  in- 
vestigations. 


MATERIAL  AND  METHODS 

The  detailed  work  has  been  done  on  three  inbred  families.  The 
achenes  were  always  germinated  in  seed  pans  in  which  the  soil  had 
been  sterilized,  or  which  had  been  filled  with  soil  near  which  no  Crepis 
plants  had  been  grown  within  the  last  few  years.  The  achenes  were 
lightly  covered  with  soil  and  watered.  The  germination  was  fairly 
rapid  and  the  seedlings  were  ready  for  transplantation  in  about  four 
weeks  from  the  date  of  sowing.  They  were  transferred  either  to  small 
cardboard  boxes  about  two  inches  square  and  planted  out  in  the  field 
or  to  4-inch  or  6-inch  pots  directly.  The  size  of  the  pot  had  very 
little  influence  on  the  early  development  of  the  plant  although,  so 
far  as  general  vigor  was  concerned,  the  plants  in  the  6-inch  pots  gave 
better  results. 

In  measuring  the  length  of  the  leaves  and  determining  their  lobe 
number,  the  plants  were  allowed  to  develop  as  far  as  possible  in  the 
rosette  stage  and  data  were  secured  before  the  central  axis  appeared 
with  the  formation  of  the  cauline  leaves.  The  length  of  the  leaf  was 
measured  on  a  centimeter  scale  and  the  number  of  lobes  counted  on 
one  side  of  the  leaf,  usually  the  left  side.  Every  lobe  which  was  sup- 
plied with  a  distinct  vein  was  given  a  unit  rank  and  in  these  calcula- 
tions all  scurs  at  the  base  of  the  leaf  and  the  secondary  lobes  attached 
to  the  main  ones  were  not  considered.  Five  leaves  were  indiscrimin- 
ately chosen  and  counts  made  upon  them. 

The  capitula  were  measured  on  the  centimeter  scale  when  they 
were  fully  open.     Flower  heads  in  Crepis  open  centripetally,  and  a 


220  University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 

flower  head  was  considered  fully  open  when  all  the  disc  florets  had 
opened  and  the  stigmas  were  projecting.  This  stage  is  usually  main- 
tained for  two  or  three  days.  Then  the  capitula  widen  and  spread  out, 
and  measurements  taken  at  this  stage  always  give  results  which  are 
about  3  mm.  more  than  the  actual  diameter  when  the  heads  are  fully 
open.  Moreover  the  flowers  open  at  about  9  a.m.  on  bright  days  and 
remain  open  till  after  3  p.m.  if  the  day  is  not  hot.  But  on  dull  and 
cloudy  days  they  open  about  10  a.m.  or  later,  and  occasionally  they 
fail  to  open  altogether.  The  25  flowers  first  formed  were  measured 
in  every  case  and  their  individual  measurements  noted.  Inflorescence 
in  Crepis  closely  follows  the  type  described  by  Gleason  (1919)  for 
Vernonia  mussurica.  The  main  axis  is  the  first  to  give  off  flowers, 
and  the  few  branches  at  the  top  are  more  or  less  leafless.  The  flowers 
form  a  more  or  less  flattened  corymb  at  the  top.  The  lower  nodes 
bear  shorter  and  frequently  less  developed  lateral  branches  which 
usually  appear  so  late  in  the  season  that  none  of  the  heads,  or  only 
a  part  of  them,  open  their  flowers  and  set  seed  before  the  plant  has 
exhausted  itself  and  dies  down.  In  Vernonia  three  types  of  varia- 
tions were  investigated :  ( 1 )  a  variation  between  the  heads  of  each 
cyme,  possibly  correlated  with  their  position  whether  terminal  or 
inferior;  (2)  a  variation  between  different  floriferous  branches  of  the 
same  plant  possibly  correlated  with  the  amount  of  available  nourish- 
ment ;  (3)  a  general  variation  between  different  individuals,  possibly 
correlated  with  the  size  and  vigor  of  the  plant  and  therefore  indirectly 
with  the  habitat.  Gleason  finds  that  within  a  single  cyme  of  from 
two  to  six  heads  the  terminal  head  is  the  largest.  In  larger  cymes, 
some  of  the  secondary  terminal  heads  are  frequently  larger  than  the 
primary  terminal  head,  the  number  of  flowers  is  greatest  for  the 
terminal  head  of  each  cyme,  but  it  is  relatively  constant  for  each 
individual  plant.  Two  sets  of  factors,  which  may  be  environmental, 
or  hereditary,  or  both,  are  involved.  One  determines  the  number  of 
heads  produced  and  the  other  the  average  number  of  flowers  in  each 
head.  These  act  upon  the  plant  independently  and  thus  give  four 
classes :  many  large  heads,  many  small  heads,  few  large  heads,  and 
few  small  heads.  This  investigator  based  his  measurements  and  con- 
clusion on  25  flowers.  Goodspeed  and  Clausen  (1915)  estimate  25  as 
the  minimum  number  on  which  to  base  any  calculations  for  flower 
size.  Goodspeed  and  Clausen  (1918)  have' described  a  mechanical 
apparatus  by  which  measurement  of  flowers  is  made.  East  uses  only 
a  millimeter  scale ;  I  have  followed  East  in  this  work. 


1923]  Bau:  Morphological  Characters  in  Crepis  Capillaris  221 

With  regard  to  the  method  of  cross-pollinating  the  plants,  both 
the  methods  suggested  by  Babcock  and  Collins  (1920)  were  tried, 
and  depollination  with  a  water  jet  has  given  results  as  good  as  emascu- 
lation, although  the  latter  method  was  employed  in  all  cases  of  critical 
investigation.  The  flowers  were  enclosed  in  translucent  paper  bags 
to  prevent  insect  pollination  and  the  achenes  gathered  before  they 
were  over-ripe  and  dropped  to  the  ground  or  were  taken  off  by  the 
wind.  It  is  fairly  easy  to  decide  whether  a  cross-pollination  has  been 
successful  or  not  because  the  involucre  assumes  an  ovoid  form  in  the 
successful  crosses,  whereas  it  remains  more  or  less  oblong  in  the  unsuc- 
cessful ones.  The  achenes,  moreover,  are  plump  and  the  ribs  marked, 
the  seed  coat  itself  being  distinctly  colored  as  compared  with  that  of 
the  unfertilized  achenes. 


INHERITANCE  OF  LENGTH  OF  LEAF 

In  Crepis  capillaris  the  first  true  leaves  are  small  (about  twice  the 
size  of  the  cotyledons),  and  there  is  a  continuous  increase  in  leaf  size 
until  the  rosette  is  formed.  Plate  42  shows  stages  of  growth  of  the 
leaves  including  the  mature  rosette  when  they  are  ready  for  measur- 
ing. Even  in  the  early  stages  the  plants  show  different  habits  of 
growth,  some  growing  erect  and  others  spreading  horizontally.  In 
one  family  especially  (20.6)  there  is  a  tendency  for  the  leaf  margins 
to  curl  downward,  thus  rendering  measurement  difficult  (plate  42y 
fig.  4).  In  the  earlier  work,  the  leaves  were  clipped  off  with  a  pair  of 
fine  scissors  close  to  the  stem  and  measured  on  a  centimeter  ruler. 
But  later  on  it  was  thought  that  injuring  the  plants  thus  might  affect 
the  result,  and  the  leaves  were  kept  intact  on  the  plant  while  the  ruler 
was  thrust  in  as  close  to  the  stem  as  possible.  Five  mature  leaves 
were  measured  at  random  and  the  average  of  the  readings  has  been 
taken  to  represent  the  mean  length  of  leaf  in  the  plant.  In  table  1  it 
will  be  seen  that  the  length  of  leaf  fluctuates  widely  from  the  mean 
as  compared  with  the  breadth.  The  variation  in  length  was  12.6  to 
23.0  cm.  in  family  20.1,  11.8  to  18.4  cm.  in  family  20.6,  15.8  to  30.7  cm. 
in  family  20.11  and  from  24.0  to  40.1  cm.  in  family  20.13.  Crosses 
were  made  between  the  20.1  family  with  a  range  from  13  to  23  cm., 
and  family  20.13  with  a  spread  of  21.0  to  40.1  cm.  with  a  view  to 
studying  the  way  in  which  the  factors  for  length  segregated.  Table 
2  gives  the  usual  biometrical  data  for  the  various  families  studied. 
This  table  indicates  that  the  factors  for  length  show  segregation  in  F2, 
but  owing  to  the  fact  that  the  environment  plays  such  a  great  part  in 


222 


University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 


determining  the  length,  it  is  difficult  to  estimate  the  number  of  factors 
involved.  (See  Hayes,  1912,  p.  34.)  Figure  1  shows  the  length 
of  leaves  typical  of  the  parent  races,  and  typical  leaves  from  the  Fx 
population.  Figure  2  shows  typical  leaves  from  plants  of  the  F2 
generation.  The  drawings  have  been  made  from  actual  prints  of 
leaves  on  photographic  paper  and  reduced  equally  in  reproduction. 


TABLE  1 
Showing  Measurements  of  Length  and  Width  of  Leaves 


20 

.1 

20 

.6 

20 

n 

20 

13 

Length 

Width 

Length 

Width 

Length 

Width 

Length 

Width 

cm. 

cm. 

cm. 

cm. 

cm. 

cm. 

cm. 

cm. 

22.2 

3.9 

18.1 

4.5 

15.8 

3.1 

29.4 

4.0 

17.3 

3.6 

15.5 

4.3 

23.3 

4.4 

34.0 

5.0 

17.2 

3.5 

14.6 

3.7 

25.5 

6.8 

35.0 

6.0 

15.0 

2.5 

16.3 

3.5 

30.7 

6.8 

30.0 

3.6 

18.4 

2.8 

11.8 

2.0 

20.0 

4.5 

40.1 

5.8 

15.5 

3.4 

16.1 

3.7 

29.5 

7.3 

26.1 

5.1 

15.6 

3.4 

16.0 

3.7 

32.2 

5.6 

37.7 

6.5 

15.6 

3.4 

14.7 

3.2 

28.6 

6.0 

26.0 

3.5 

20.0 

3.4 

18.4 

4.5 

18.5 

5.0 

24.0 

3.0 

23.0 

4.4 

13.2 

2.5 

28.6 

6.0 

28.0 

6.0 

19.8 

2.9 

14.9 

3.6 

33.0 

4.5 

12.6 

2.0 

15.8 

3.1 

34.0 
24.0 
34.0 
29.0 
31.0 
31.5 
23.0 
31.0 
21.0 
21.6 
29.5 

6.0 
3.5 
5.6 
5.0 
4.0 
3.8 
3.0 
5.0 
2.5 
3.0 
4.3 

Total: 

212.2 

35.8 

185.4 

42.3 

252.7 

55.5 

652.9 

98.7 

Average : 

17.7 

3.0 

15.45 

3.5 

25.3 

5.5 

29.7 

4.5 

It  should  be  stated  that  the  plants  of  the  F2  population  were  grown 
in  4-inch  pots  while  those  of  the  parent  races  and  Fx  population 
were  in  6-inch  pots.  However,  the  F2  plants  were  all  grown  under 
uniform  conditions  so  that  the  evidence  of  segregation  in  both  leaf 
length  and  number  of  lobes  may  be  referred  to  genetic  differences 
among  the  F2  plants. 


1923] 


Ban:  Morphological  Characters  in  Crcpis  Capillaris 


223 


INHERITANCE  OF  THE  NUMBER  OF  LOBES 

The  problem  of  the  number  of  lobes  on  the  leaves  resolves  itself 
into  four  distinct  subheads.  The  first  of  these  involves  the  question 
whether  the  leaf  shall  be  considered  lobed  at  all.  There  are  families 
in  which  the  lobing,  if  present,  is  so  shallow  that  the  leaves  would  be 
described  as  entire  or  merely  dentate.     This  type  is  designated  as 


TABLE  2 
Showing  the  Eesults  of  Crossing  for  Inheritance  of  Leaf  Length 


Nature  of  Cross 

Generation 

Mean 

Stand,  deviation 

Coef.  of  Var. 

20.1x20.13 

Pi 
Pi 

Fl 

F2 

17.9  ±  .588 
29.7  ±  .699 
29.0  db  .282 
14.9  ±  .137 

2.89  db  .468 
4.97  ±  .495 
2.33  ±  .188 
5.28  ±  .097 

16.1 
16.7 

8.0 
35.4 

Applying  Castle's  formula 


(29.7  -  17.9)2        139.24 


8(5.282  -  2.332)        179.2 


Factors  responsible  for  length  =  1  factor. 

This  result  is  very  improbable,  but  the  results  can  be  interpreted  on  a  modified 
dihybrid  ratio  of  9:6:1  where  the  two  single  homozygous  genotypes  give  identical, 
effects.   On  this  ratio  and  from  a  study  of  the  data,  the  result  may  be  stated  thus: 

A  B  =  9,  leaf  length  from    6  —  18  cm. 

A  b  =  3,  leaf  length  from  19  —  25  cm. 

a  B  =  3,  leaf  length  from  19  —  25  cm. 

a  b  =1,  leaf  length  from  26  —  34  cm. 

Where  factors  A  and  B  stand  for  two  independent  factors  in  the  absence  of  both 
of  which  the  double  recessive  a  b  is  obtained: 

Observed  numbers:    491    :    158    :   27 
Calculated  numbers:  378    :   252    :   42. 

simplex  in  the  accompanying  account.  There  is  another  type  where 
the  lobes  are  distinct  and  simple  and  look  like  the  steps  on  a  ladder. 
This  is  designated  as  the  scalaris  type.  A  third  type  has  a  complex 
type  of  lobes  where  the  scalaris  type  of  lobing  is  surmounted  by 
smaller  secondary  lobules  or  wings.  The  second  subhead  refers  to 
the  incision  or  depth  of  lobing.  In  the  families  studied  the  lobing 
extended  halfway  from  the  margin  to  the  mid-rib  or  completely  to 
the  mid-rib.  The  third  subhead  concerns  number  of  lobes  on  the  leaf 
and  the  fourth  refers  to  the  character  which  is  shown  when  the  "second- 
ary lobules   instead   of   remaining   attached   to   the   main   lobes   are 


224 


University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 


separated  and  form  independent  lobes  attached  to  the  mid-ribs.  The 
first  of  these  is  the  major  character  because,  without  a  tendency  to 
form  the  lobes,  the  rest  of  the  factors  could  not  express  themselves. 
But  the  remaining  three  subheads  behave  as  separate  groups  of  factors, 
the  depth  of  incision  having  an  independent  action  on  the  leaf  as  do 
the  other  two  characters  mentioned  above.  One  thing,  however,  was 
clear  from  the  studies  made,  and  that  was  the  complex  way  in  which 


Fig.  la.  A  typical  leaf  of  the  race  with  long  leaves  and  many  lobes,  g.  A 
typical  leaf  of  the  race  with  short  leaves  and  few  lobes,  o-f.  Typical  leaves  from 
different  plants  of  the  Fx  generation,     c.  X  %. 


each  of  these  characters  was  inherited.  That  these  groups  of  charac- 
ters are  inherited  in  a  Mendelian  fashion  cannot  be  doubted,  but  the 
work  has  not  advanced  enough  to  estimate  with  certainty  the  number 
of  factors  involved  in  these  cases,  except  in  the  number  of  lobes,  which 
has  been  more  extensively  studied. 

The  same  families  that  furnished  material  for  studying  the  inheri- 
tance of  length  have  been  used  for  studying  the  lobe  numbers.  Table 
3  shows  the  lobe  numbers  of  the  various  families  handled  in  this  work. 
The  same  illustrations,  figures  1  and  2,  show  the  nature  of  lobing  and 
the  number  of  lobes. 


1923] 


Emi:  Morphological  Characters  in  Crepis  Capillaris 


225 


TABLE  3 

Showing  the  Kesults  of  Crossing  for  Inheritance  of  Number  of  Lobes 


Nature  of  Cross 

Generation 

Mean 

Stand,  deviation 

Coef.  of  Var. 

20.1  x20.13 

Pi 

8.9    ±  .352 

1 .  73  ±  .  248 

19.4 

Pi 

11.3    ±  .171 

1.21  ±  .134 

10.7 

Ft 

11.17  ±  .156 

1.37  ±  .110 

12.2 

F2 

8.1     ±  .087 

3.36  ±  .061 

41.5 

Applying  Castle's  formula  the  number  of  factors  would  be 

(11.3  -8.9)2  5.76 


8(3.362  -  1.372)       75.2 


an  obvious  impossibility 


Fig.  2.  — Typical  leaves  from  different  plants  of  the  F2  generation,     c.  X  %• 

The  data  can  be  interpreted  on  a  four  factor  hypothesis  where 
each  factor  in  a  homozygous  condition  contributes  two  lobes  and,  in  a 
heterozygous  condition 
formula  would  be, 


,  one  lobe.     On 

this  1 

a    a   b   b    c    c    d 

d 

5 

a    a   b  B    c    c    d 

d 

6 

a    a  B  B    c    c    d 

d 

7 

a  A  B  B    c    c    d 

d 

8 

A  A  B  B    c    c    d 

d 

9 

A  A  B  B  C    c    d 

d 

10 

A  A  B  B  C  C    d 

d 

11 

A  A  B  B  C  C  D 

d 

12 

A  A  B  B  C  C  D 

D 

13 

and  the  data  on  this  hypothesis  would  give  a  curve  which  simulates 
the  normal  curve  of  error  with  the  mode  at  8. 


226  University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 

From  the  data  presented  in  table  3,  it  is  fair  to  conclude  that 
there  is  segregation  with  respect  to  mean  lobe  number  in  F2.  Both 
the  F1  and  F2  are  intermediate  between  the  two  grandparent  types 
and  in  the  latter  there  is  no  transgressive  segregation  on  the  side  of 
the  higher  number  of  lobes.  The  number  of  lobes  ranges  from  6  to  13 
in  the  F2  family  21.141  and  arranging  the  plants  in  class  groups  their 
distribution  is  as  follows,  the  mean  being  at  9. 


6 

31 

7 

42 

8 

54 

9 

35 

0 

47 

1 

37 

2 

9 

3 

1 

256 

This  tabulation  shows  that  the  inheritance  of  lobe  number  is  compli- 
cated ;  and,  while  more  of  the  plants  show  the  lobe  number  of  the  lower 
numbered  parent,  the  majority  of  them  are  intermediate  as  required 
by  the  hypothesis  of  multiple  factors.  The  same  remarks  apply  to  the 
other  F2  populations  studied,  and  there  must  be  at  least  four  factors 
responsible  for  number  of  lobes  in  the  leaves. 

The  length  of  the  leaf  has  little  or  no  influence  upon  the  number  of 
lobes  in  the  leaves.     The  accompanying  correlation  chart,  table  4, 


TABLE  4 

Correlation  Table  for  Number  of  Lobes  (x)  and  Length  of  Leaf  in  cm.  (y) 

Family   21.140 


4 

5 

6 

7 

2y 

8-11 

10 

4 

14 

11-14 

1 

15 

25 

41 

14-17 

11 

17 

1 

29 

17-20 

8 

46 

6 

60 

20-23 

9 

54 

4 

67 

23-26 

9 

38 

1 

48 

26-29 

4 

8 

0 

12 

2X 

1 

66 

192 

12 

rxv  =  0.2302  ±  0.0388 


1923]  Rau:  Morphological  Characters  in  Crepis  Capillaris  227 

constructed  for  family  21.140,  shows  that  the  correlation  between  the 
two  is  very  low.  For  purposes  of  calculation,  length  of  lobe  is  ex- 
pressed in  round  numbers  of  centimeters,  the  fraction  being  treated 
as  one  when  more  than  half  and  ignored  when  less  than  that  amount. 
The  absence  of  influence  of  length  of  leaf  on  number  of  lobes  is 
also  illustrated  by  a  comparison  of  the  leaf  outlines  which  show  practi- 
cally the  same  number  of  lobes  on  leaves  of  different  lengths  and  in 
other  cases  different  numbers  of  lobes  on  leaves  of  practically  the  same 
length.  From  an  extended  study  of  the  data  as  well  as  from  observa- 
tions in  the  field  and  green  house  on  various  races  of  Crepis  capillaris, 
I  am  led  to  conclude  that  number  of  lobes  is  a  definitely  heritable 
character  and  is  not  influenced  by  length  of  leaf,  by  soil  or  by  any 
other  environmental  conditions  under  which  the  plant  is  grown. 


INHERITANCE  OF  SIZE  OF  CAPITULUM 

Goodspeed  and  Clausen  (1915)  have  determined  a  number  of  fac- 
tors which  influence  flower  size  in  Nicotiana.  Under  the  heading, 
"age  of  plant,"  they  have  considered  the  difference  in  size  of  flowers 
borne  early  in  the  season  as  compared  with  those  borne  late  in  the 
season  on  the  same  plants  as  well  as  the  difference  in  size  of  flowers 
during  the  first  blooming  season  of  the  plant  compared  with  that  of 
flowers  produced  the  next  year  and  on  the  same  plants  cut  back  and 
sprouting  from  the  roots.  Under  the  heading  "age  of  flower,"  they 
include,  first,  a  consideration  of  the  difference  in  the  size  of  flowers 
borne  on  the  terminal  inflorescences  first  coming  out  of  the  stem  and 
those  borne  at  the  same  time  on  laterals  and  seconds,  and  (2),  the 
influence  of  age  on  the  individual  flower  by  comparing  measurements 
of  flowers  fully  opened  before  and  after  shedding  pollen.  Other  factors 
such  as  influence  of  removal  of  flowers  and  developing  seed  capsules, 
the  behavior  of  cuttings  under  various  conditions,  and  the  influence  of 
soil  fertility  were  also  studied.  They  find  that  the  flowers  produced 
later  in  the  season  have  usually  been  of  smaller  size.  By  removing  all 
flowers  as  fast  as  they  are  produced,  they  find  it  possible  to  keep 
the  flower  size  nearly  equal  to  that  of  the  first  flowers  produced  and 
were  able  in  some  cases  to  double  the  length  of  a  plant 's  life.  During 
the  period  which  elapses  from  the  time  a  flower  is  fully  opened  to  the 
time  when  pollen  is  shed,  there  is  a  considerable  increase  in  corolla 
spread,    and    associated    with    it,    little    or    no    increase    in    corolla 


228  University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 

length.  Soil  also  had  a  great  influence  in  their  experiments  in  deter- 
mining the  size  of  the  flowers.  ' '  The  conclusion  seems  irresistible  that 
flower  size  in  Nicotiana  is  not  so  constant  as  it  has  been  assumed  to  be, 
but  that  it  is  affected  by  a  number  of  conditions  and  that  at  least 
some  of  these  may  not   affect  the   length   and   spread   in  the   same 


Influence  of  Age  of  Plant 

In  Crepis  capillaris,  the  25  capitula  first  formed  are  usually  very 
uniform  and  show  a  very  narrow  range  of  variation.  The  terminal 
flower  is  usually  the  largest,  although  the  next  two  flowers  below  it 
are  of  the  same  size  in  many  instances;  but  usually  there  is  a  signifi- 
cant difference  of  1  mm.  when  a  large  number  of  flowers  are  measured. 
The  flowers  were  pulled  off  and  measured  in  every  instance,  which 
eliminated  to  a  large  extent  the  possibility  of  the  flowers'  growing 
slightly  smaller.  As  a  rule  the  25  flowers  required  were  measured  in 
about  a  week's  time,  although  the  plant  normally  continues  to  flower 
for  about  four  to  five  weeks.  Flowers  measured  at  the  end  of  a  season 
are  about  15  to  20  per  cent  smaller  than  those  measured  at  the  begin- 
ning and,  owing  to  the  setting  of  seed  and  senility  of  the  plant,  all 
the  buds  formed  do  not  open.  In  an  experiment  which  was  carried 
on  to  measure  the  entire  lot  of  flowers  that  were  produced  on  6  plants 
of  a  strain,  the  plants  started  flowering  on  the  tenth  of  February  and 
continued  till  the  end  of  April.  Comparing  the  early  flowers  with 
those  formed  later,  the  size  of  the  latter  is  smaller.  But  this  reduction 
is  not  so  great  as  in  the  case  of  plants  from  which  no  flowers  are 
removed.  Two  things  can  be  noted,  however,  in  the  flowers  formed 
later.  The  number  of  flower  heads  that  open  on  any  given  day  is  less 
than  before  and  the  number  of  florets  per  head  is  significantly  smaller, 
the  capitulum  showing  a  more  open  center.  The  actual  size  of  the 
floret  is  not  perceptibly  reduced  and  this  accounts  for,  the  fact  that 
the  size  of  the  flowers  remains  fairly  constant.  Another  character 
that  can  be  seen  in  the  flower  heads  formed  later  is  the  slender  elon- 
gated stalks  on  which  they  are  borne  as  compared  with  the  robust  stalks 
of  the  earlier  formed  flower  heads,  while  in  many  cases  the  internodes 
between  the  flower  stalks  are  longer  in  the  later  formed  flowers. 


1923] 


Ban:  Morphological  Characters  in  Crcpis  Capillaris 


229 


Position  of  Capitulum  upon  the  Plant  as  a  Factor 

The  position  of  the  capitulum  cannot  always  be  categorically  sep- 
arated from  the  influence  of  age  of  plant.  Two  distinct  facts,  however, 
are  involved  in  this  group.  The  first  is  the  position  of  the  capitulum 
with  reference  to  its  origin,  which  may  be  in  the  axils  of  the  lower 
or  the  upper  leaves  or  in  the  terminal  cyme.  The  second  is  the 
position  of  the  capitulum  with  reference  to  the  cyme  itself  of  which 
it  forms  a  part.     Figure  3  shows  a  diagrammatic  representation  of 


Fig.  3.  — Diagrammatic  representation  of  the  inflorescence  in  Crepis  capillaris. 
Numbers  indicate  diameter  of  capitula  of  a  single  plant  measured  in  centimeters. 


230  University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 

the  inflorescence  and  furnishes  the  measurements  of  the  diameters 
of  individual  capitula  of  a  single  plant.  Comparing  the  individual 
cymose  clusters,  the  terminal  cluster  has  the  largest  central  flowers 
closely  followed  by  the  next  few  lower  clusters.  As  the  measure- 
ments are  followed  farther  down,  the  central  capitulum  becomes 
slightly  smaller.  The  lateral  capitula  are  generally  smaller  thai 
the  central  capitulum  in  each  cluster,  but  at  times  they  may  attain 
to  the  same  size,  especially  in  the  uppermost  cymes.  Very  rarely 
they  are  larger  than  the  central  capitulum  of  the  cyme  of  which 
they  are  laterals.  The  central  capitula  of  the  lower  cymes  may 
be  larger  than  the  lateral  capitula  of  the  upper  cymes.  In  com- 
paring flower  heads  as  to  size,  however,  the  facts  that  all  the  capitula 
do  not  ripen  at  the  same  time  and  that  the  age  of  the  plant  is  a 
factor  causing  variation  should  be  kept  in  mind.  Moreover,  in  this 
group  of  measurements,  the  flowers  were  pulled  off  for  measuring, 
and  this  has  a  tendency  to  keep  the  inflorescence  active  for  a  longer 
time  and  to  maintain  the  flower  size,  as  has  been  noted  by  Goodspeed 
and  Clausen.  The  facts  as  to  variation  of  size  in  the  flowers,  due  to 
the  age  and  position  of  the  flower,  may  be  summarized  by  saying 
that,  in  plants  allowed  to  flower  normally,  the  terminal  flower  head 
is  usually  the  largest,  closely  followed  by  the  second  and  third  flower 
heads,  after  which  the  size  becomes  slightly  smaller.  The  relative 
size  of  the  flowers  on  the  lower  branches  is  similar,  but  the  terminal 
flowers  on  the  lower  branches  are  smaller  than  the  terminal  flower  of 
the  whole  plant  or  than  those  terminal  flowers  which  arise  from 
branches  in  the  axils  of  the  uppermost  leaves. 


Environmental  Factors 

Light. — With  regard  to  the  effect  of  light  on  the  flowering  of 
plants,  some  interesting  results  have  been  obtained.  Klebs  (1918) 
in  his  work  on  Sempervivum  divided  the  process  of  flower  formation 
into  three  distinct  stages :  (1)  production  of  the  condition  of  ripeness 
to  flower,  (2)  formation  of  flower  primordia,  and  (3)  development 
of  flower  clusters  and  elongation  of  the  axis.  He  found  that  light  is 
the  dominant  factor  in  determining  all  three  stages.  More  recently 
Garner  and  Allard  (1920)  have  published  their  opinion  that  the  three 
primary  factors  that  enter  into  the  action  of  light  upon  plants  are  (1) 
intensity  of  the  light,    (2)   quality,  that  is,  the  wave  length  of  the 


1923]  Bau:  Morphological  Characters  in  Crepis  Capillaris  231 

radiation,  and  (3)  duration  of  exposure.  They  conclude  that  the 
relative  length  of  day  is  a  factor  of  prime  importance  in  the  growth 
and  development  of  plants,  particularly  with  respect  to  sexual  repro- 
duction, and  in  1922  they  confirmed  and  amplified  their  work.  I 
have  been  able  to  confirm  this  work  to  a  certain  extent.  A  culture 
of  plants  growing  in  the  greenhouse  was  close  to  an  electric  lamp 
used  to  maintain  a  constant  temperature  in  a  chamber  close  by,  and 
the  plants  that  were  closest  to  this  lamp  flowered  first,  the  arc  of 
flowering  spreading  out  centrifugally.  After  some  time  all  the  plants 
that  were  near  the  lamp  had  flowered,  although  the  rest  of  the  cultures 
took  nearly  two  months  longer  to  produce  flowers.  Moreover,  the 
plants  that  bloomed  first  were  in  a  comparatively  disadvantageous 
position  during  the  day,  so  that  the  effect  of  the  artificial  illumination 
on  the  flowering  of  the  plants  is  all  the  more  striking.  This  observa- 
tion was  repeated  in  an  attempt  to  hasten  the  process  of  flower  forma- 
tion. Two  strains  of  plants,  0215  and  0217,  which  were  both  Fx 
progeny  of  crosses  made  by  me,  were  growing  very  slowly  and  were 
still  in  the  rosette  stage  by  the  end  of  March  of  this  year  due  to  the 
cold  winter.  In  order  to  hasten  their  growth  and  obtain  seed  for 
growing  an  F2  population,  a  few  of  them  were  placed  three  feet  below 
a  300  Watt  electric  lamp  surrounded  by  a  reflector  every  day  from 
6  p.m.  to  8  a.m.  the  next  day.  Some  of  them  shot  out  flower  buds  in 
about  three  weeks  from  the  time  the  experiment  was  started.  The 
rest  of  the  plants  in  the  same  families  which  were  not  subjected  to 
artificial  light  had  in  many  cases  not  started  to  send  up  the  central 
floriferous  axils.  The  heat  from  the  lamp  may  also  have  had  a  slight 
effect. 

Moisture. — The  plants  as  they  grow  in  pots  in  the  greenhouse  are 
not  subject  to  much  variation  in  soil  moisture  because  they  are 
watered  regularly  and  the  minimum  soil  moisture  necessary  for  proper 
growth  is  usually  maintained.  The  case  of  the  plants  grown  in  the 
field,  however,  was  different  because  irrigation  water  was  applied 
periodically,  and  owing  to  the  variation  in  temperature  of  the  days 
intervening  between  two  successive  irrigations,  the  soil  moisture  was 
neither  constant,  nor  was  it  always  above  the  minimum  water  require- 
ments of  the  plants.  Consequently,  the  flowers  gradually  got  smaller 
as  time  elapsed  after  irrigation  until,  during  the  hottest  part  of 
the  day,  the  plants  would  show  signs  of  withering.  Measurements 
were  taken  at  this  period  and  showed  comparatively  the  smallest  size 
in  the  diameter  of  the  capitula.      This  difference  went  up  usually 


232 


University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 


to  a  maximum  of  4  mm.,  but  usually  it  ranged  between  2  mm.  and 
3  mm.,  and  more  often  reached  the  lower  limit.  If  at  this  stage 
the  land  was  irrigated,  the  measurements  taken  the  next  day  in- 
variably showed  a  rise.  The  following  data  taken  on  plants  of  the 
same  population  both  before  and  after  irrigation  illustrate  this  point. 

-Culture  Hsu  20.1- 


Before  Irrigation 

After  Irrigation 

Number  of  plant 

Number  of  flowers 
measured 

Average  diameter 
in  cm. 

Number  of  flowers 
measured 

Average  diameter 
in  cm. 

3 
9 

27 
38 
49 
59 
77 
99 

4 
4 
4 
3 
3 
5 
4 
3 

1.87 
1.97 
1.90 
2.00 
1.96 
1.98 
2.05 
2.00 

5 
5 
6 
5 
4 
4 
5 
5 

2.16 
2.22 
2.10 
2.22 
2.25 
2.05 
2.16 
2.16 

Total 

30 

1.95 

39 

2.16 

There  is  an  average  difference  of  0.21  cm.  or  approximately  2  mm. 


A  Cross  Involving  Difference  in  Head  Size 

This  particular  work  was  started  in  the  summer  of  1921  and  was 
carried  only  to  the  F1  stage.  Two  strains  were  chosen,  one  having  a 
diameter  ranging  from  17  to  25  mm.,  and  the  other  from  21  to  36  mm. 
These  races  had  undergone  a  preliminary  purification  for  size  of  flower 
head.  The  F±  was  intermediate  and  the  mean  of  the  Fx  population 
was  closer  to  the  mean  of  the  smaller  parent  than  that  of  the  larger 
parent.  The  data  that  have  been  secured  on  this  work  are  given  in 
table  5.  Other  crosses  have  given  similar  results,  but  as  the  parent 
strains  did  not  differ  in  any  marked  degree,  the  Fx  obtained  shows 
about  the  same  size  of  head  diameter. 


1923] 


Rau:  Morphological  Characters  in  Crepis  Capillaris 


233 


TABLE  5 
Showing  Results  of  Crossing  for  Diameter  of  Capitulum 


Frequencies 

Diam.  of  heads  in  mm. 

H21.1 

B21.13 

Fi  hybrids 

17 

8 

18 

74 

19 

266 

17 

20 

444 

42 

21 

343 

19 

85 

22 

368 

53 

98 

23 

278 

60 

142 

24 

149 

33 

103 

25 

71 

36 

94 

23 

24 

16 

32 

27 

29 

12 

28 

25 

29 

7 

30 

10 

31 

12 

32 

11 

33 

13 

34 

2 

35 

36 

1 

Mean 

21.27  ±  .027 

25.37  ±  .131 

22.96  ±  .048 

Stand.  Dev. 

1.84  ±  .019 

3.52  ±  .093 

1.81  ±  .036 

Coef.  Var. 

8.6 

13.87 

7.8 

DISCUSSION  OF  RESULTS 

1.  The  leaves  of  Crepis  capillaris  vary  in  outline  from  a  simplex 
through  a  scalaris  to  a  bipinnate  type  of  lobing.  In  the  first  ease,  as 
evidenced  by  one  of  the  parents  used  in  the  cross  (fig.  1)  the  outline 
is  more  or  less  entire,  while  the  other  parent  in  this  cross  represents 
the  scalaris  type.  The  Fx  progeny  obtained  exhibited  considerable 
variation  but  were  always  intermediate  between  the  two  extreme  types. 
In  the  F2  there  was  decided  segregation  and  since  only  one  plant  out 
of  over  250  showed  characters  almost  similar  to  one  grandparent, 
there  must  be  more  than  one  factor  responsible  for  the  occurrence  of 
lobes  as  well  as  for  the  number  of  lobes.     The  cross  20.1  X  20.13  has 


234 


University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 


given  an  intermediate  number  of  lobes  in  Fx  generation  and  in  F2 
the  progeny  ranged  from  one  parent  type  to  the  other.  Out  of  the 
250  F2  plants  studied  not  one  fully  represented  the  grandparent  types, 
and  on  mathematical  considerations  there  must  be  at  least  four  factors 
responsible  for  this  condition.  Shull  (1918)  in  his  work  on  the  leaf 
forms  of  the  Shepherd 's  Purse  has  formulated  a  two  factor  hypothesis, 
the  double  dominant  homozygote,  the  two  single  dominant  homozygotes 
and  the  double  recessive,  giving  the  four  classes  which  he  obtained. 
With  regard  to  the  work  on  the  length  of  the  leaf,  it  has  been  found 
that,  as  compared  to  the  length,  the  breadth  of  a  leaf  is  a  much  more 
constant  character  as  shown  by  table  6.    The  data  for  this  table  were 


TABLE   6 
Showing  Average  Length  and  Width  of  Leaves  in  100  Plants  of  Family  20.140 


Length  in  cm. 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

Number  of  plants 

2 

6 

10 

6 

6 

10 

15 

13 

11 

13 

6 

2 

Width  in  cm. 

2.0 

2.2 

2.4 

2.6 

2.8 

3.0 

3.2 

3.4 

3.6 

Number  of  plants 

13 

11 

26 

27 

8 

9 

0 

5 

1 

obtained  from  a  family  of  plants  selected  at  random.  This  observation 
is  in  accordance  with  the  reports  of  some  other  investigators.  More- 
over, the  length  of  a  leaf  is  more  markedly  susceptible  to  environ- 
mental influences  and  fluctuations  due  to  modifications  will  profoundly 
interfere  with  estimating  the  effects  of  recombinations.  It  is  therefore 
believed  that  races  should  be  purified  for  the  breadth  factor  rather 
than  for  the  length  factors  for  facilitating  studies  in  this  direction. 
During  the  progress  of  the  work,  several  crosses  were  made  between 
strains  of  Crepis,  and  some  of  the  strains  were  inbred.  The  result  in 
many  cases  was  comparable  to  the  results  of  inbreeding  in  corn.  As 
Collins  (1920)  has  noted,  plants  of  inbred  strains  may  not  put  out 
flowers  at  all,  or  if  they  do,  very  few  of  the  heads  set  seed.  Some  of 
these  are  viable  and  give  rise  to  seedlings  which  may  not  thrive  very 
well  unless  they  are  given  special  care.  They  are  not  as  strong  as  those 
obtained  from  hybrid  plants.  When  they  have  grown  beyond  the 
seedling  stage,  they  sometimes  stay  in  the  rosette  stage  much  longer 
than  is  usual  and  the  vegetative  period  is  consequently  prolonged.  One 
strain  remained  in  the  rosette  stage  and  produced  no  flowers  although 
it  had  been  growing  for  over  a  year  and  a  half.  Other  abnormalities 
have  also  been  noted,  such  as  vegetative  proliferation  and  fasciation 
of  stems  and  peduncles.      Often  the  flower  heads  are  fasciated  and 


1923]  Rau:  Morphological  Characters  in  Crepis  Capillaris  235 

flattened  on  two  sides  assuming  the  shape  of  an  oval  as  opposed  to 
the  normal  round  shape  and  at  times,  owing  to  a  shortening  of  the 
pedicels,  two  or  three  flowers  appear  to  be  joined  together.  All  these 
malformations  have  been  noted  in  one  or  another  of  the  cultures,  and 
emphasize  strongly  the  effects  of  inbreeding  in  bringing  to  light 
undesirable  recessive  characters  which  are  disadvantageous  to  the 
growth  of  the  individual  plant. 

The  outcome  of  this  portion  of  the  work  has  given  results  in  no  way 
contradictory  to  the  conclusions  arrived  at  by  other  investigators  who 
have  relied  upon  multiple  factors  as  an  explanation  of  inheritance  of 
quantitative  characters.  As  the  experiment  has  not  been  carried  to 
the  F3  stage,  it  is  not  possible  to  state  whether  this  material  will  yield 
results  entirely  consistent  with  the  requirements  (East,  1916)  of  the 
multiple  factor  hypothesis.  But  as  far  as  the  results  go,  they  are  in 
agreement  with  the  explanation  suggested  that  inheritance  of  the 
number  of  lobes  in  Crepis  capillaris  is  a  Mendelizing  quantitative 
character  and  that  it  is  controlled  by  many  factors  which  affect 
occurrence  of  lobes,  depth  of  the  incisions,  number  of  lobes,  and  shape 
of  the  lobes. 

It  may  be  here  noted,  in  passing,  that  in  a  work  of  this  nature  a 
certain  amount  of  discretion  is  necessary  in  determining  the  class  to 
which  a  given  individual  belongs.  Classification  of  the  shape  of  a 
leaf  and  the  exact  number  of  its  lobes  are,  to  a  certain  extent,  decided 
by  the  investigator,  who  can  handle  them  quickly  as  he  gains  practice. 
Moreover,  the  exact  times  when  the  measurements  are  to  be  taken 
are  more  or  less  fixed  by  the  investigator  himself,  who  should  try  to 
secure  as  uniform  material  as  possible  in  the  several  generations. 
East  (1921)  has  raised  a  similar  point  in  his  work  as  regards  the 
personality  of  the  investigator.  He  says,  ' '  I  believe  that  in  such  work 
as  this,  the  investigator  who  lives  with  his  plants  in  the  field,  who 
uses  all  the  quantitative  data  at  his  command,  but  who,  nevertheless, 
brings  to  his  aid  all  the  somewhat  intangible  facts  that  intimate  experi- 
ence gives  him  is  able  to  come  to  a  better  realization  of  the  truth  than 
one  who  works  on  cold  data  obtained  by  others. ' ' 

2.  Size  of  capitulum  is  a  character  which  is  controlled  by  genetic 
factors,  and  it  is  fairly  constant  for  a  given  family.  It  is  practically 
independent  of  the  size  of  the  plant  and  it  cannot  fall  below  a  certain 
minimum.  It  is  also  independent  of  the  number  of  capitula  on  the 
entire  plant  or  the  number  of  florets  per  flower  head.  It  is  similarly 
uninfluenced  by  the  shape  of  the  plant.  The  tall,  erect,  vertical  type 
of  plants,  and  the  bushy  spreading  type  of  plants  (pi.  43)  have  given 


236  University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 

sizes  of  flowers  which  are  practically  identical  (see  East,  1921,  p.  329) 
and  while  casual  observation  leads  me  to  believe  that  the  number  of 
flowers  per  plant  and  the  number  of  florets  per  head  vary  directly 
with  the  size  and  shape  of  the  plant,  the  diameter  of  the  flower  heacL 
is  not  subject  to  influence  by  any  one  of  these  three  factors  and  is 
relatively  stable.  (See  Stout,  1918.)  The  only  factor  that  has  been 
found  to  influence  the  size  of  the  flower  heads  is  the  moisture  content 
of  the  soil.  The  drier  the  soil  the  smaller  the  heads  become.  Here 
the  plants  in  pots  have  an  advantage  because  the  soil  is  never  allowed 
to  become  dry  and  the  slight  variations  of  moisture  to  which  the  plants 
in  pots  are  subject  do  not  affect  the  diameter  of  the  flower  heads  to 
any  appreciable  extent.  The  results  obtained  from  field  plants  are 
strictly  comparable  among  themselves,  however,  since  all  the  strains 
are  subject  to  the  same  unfavorable  environmental  influences  and  as 
such  give  results  strictly  comparable. 


SUMMARY  AND  CONCLUSIONS 

1.  Crepis  capillaris  has  been  found  to  be  a  valuable  species  for 
genetic  investigations  because  it  is  a  wild  plant  which  has  not  been 
subjected  to  conscious  selection  by  human  agency. 

2.  It  can  be  cross-fertilized  and  the  progeny  derived  from  such 
cross-fertilization  is  fertile  inter  se  and  gives  viable  seed. 

3.  Several  characters  in  the  plant  are  constant  and  breed  true  when 
the  material  has  been  purified  to  bring  it  into  a  homozygous  condition 
for  the  character  in  question. 

4.  Continual  selfing  of  the  plant  is  followed  by  the  usual  symptoms 
of  such  treatment  in  naturally  cross-fertilized  species,  resulting  in 
reduced  vitality,  arrested  development  at  the  rosette  stage,  formation 
of  many  sterile  flowers,  few  viable  achenes,  vegetative  proliferation 
and  fasciation  of  the  capitula  and  the  stem. 

5.  Three  quantitative  characters  were  studied  in  this  plant:  the 
length  of  the  leaf,  the  number  of  lobes  in  the  leaves,  and  the  diameter 
of  the  flower  heads. 

6.  Length  of  leaf  is  a  heritable  character,  but  the  environment 
has  a  very  great  influence.  The  resulting  fluctuating  variability  is 
so  great  that  although  crosses  have  been  made  for  studying  the  type 
of  inheritance,  it  is  difficult  to  classify  and  segregate  the  F2  progeny. 

7.  In  inheritance  studies,  width  of  leaf  is  a  better  index  of  leaf 
size  than  length. 


1923]  Eau:  Morphological  Characters  in  Crepis  Capillaris  237 

8.  Number  of  lobes  per  leaf  is  constant  for  any  given  race  of  plants 
and  the  character  is  determined  by  four  sets  of  factors : 

(a)  The  group  of  factors  for  presence  of  lobes. 

(b)  The  group  of  factors  for  depth  of  the. incisions. 

(c)  The  group  of  factors  for  number  of  lobes. 

(d)  The  group  of  factors  for  extension  by  which  the   secondary 

lobules  are  developed  into  lobes. 
9.  Of  these  the  group  of  factors  for  number  of  lobes  consists  of 
at  least  four  interacting  factors.     The  Fx  in  these  crosses  was  found 
to  be  intermediate  and  F2  showed  segregation. 

10.  Races  of  Crepis  capillaris  with  different  diameters  of  capitula 
were  isolated  and  when  crosses  were  made  between  such  races  the 
diameter  of  the  capitula  of  Fx  was  found  to  be  intermediate  between 
the  two  parents.  The  work  has  not  progressed  far  enough  to  study  the 
F2  plants  and  determine  the  type  of  segregation. 

11.  As  far  as  studied,  environment,  except  moisture,  has  very  little 
influence  on  the  size  of  capitula, 


LITERATURE  CITED 
Babcock,  E.  B. 

1920.     Crepis,  a  promising  genus  for  genetic  investigations.     Am.  Naturalist, 
vol.  54,  pp.  270-276. 
Babcock,  E.  B.  and  Collins,  J.  L. 

1920.  Interspecific    hybrids    in    Crepis.      I.      C.    capillaris    (L)    Wallr.  X  C. 

tectorum  L.    Univ.  of  Calif.  Publ.  in  Agr.  Sci.,  vol.  2,  pp.  191-204. 
Beer,  Eudolf 

1912.     Studies   in   spore   development,    2.     Annals   of  Botany,    vol.    26,   pp. 
705-726. 
Castle,  W.  E. 

1921a.     On  a  method  of  estimating  the  number  of  genetic  factors  in  cases 
of  blending  inheritance.     Science,  n.s.,  vol.  54,  pp.  93-96. 
Castle,  W.  E. 

19216.     An  improved  method  of  estimating  the  number  of  genetic  factors 
concerned   in    cases   of   blended   inheritance.      Science,   n.s.,    vol. 
54,  p.  225. 
Clausen,  E.  E.  and  Goodspeed,  T.  H. 

1921.  Inheritance  in  Nicotiana  taoacum  II.  .  On  the  existence  of  genetically 

distinct    red-flowering    varieties.      Am.    Naturalist,    vol.    55,    pp. 
328-334. 
Collins,  J.  L. 

1920.     Inbreeding  and  crossbreeding  in  Crepis  capillaris   (L)    Wallr.  Univ. 
Calif.  Publ.  Agr.  Sci.,  vol.  2,  pp.  205-216. 
Digby,  L. 

1914.     A   critical  study  of  the   cytology  of  Crepis  virens.     Archiv   f.   Zell- 
forsch.,  Bd.  12,  pp.  97-146. 
East,  E.  M. 

1916.        Studies    on    size    inheritance    in    Nicotiana.      Genetics,    vol.    1,    pp. 
164-176. 


238  University  of  California  Publications  in  Agricultural  Sciences         [Vol.  7 

East,  E.  M. 

1921.  A   study   of  partial   sterility   in   certain   hybrids.      Genetics,   vol.    6, 

pp.  311-365. 
Garner,  W.  W.  and  Allard,  H.  A. 

1920.     Effect  of  the  relative  length  of  day  and  night  and  other  factors  of 

the   environment   on   growth   and   reproduction  in   plants.     Jour. 

Agr.  Kes.,  vol.  18,  pp.  553-606. 
Garner,  W.  W.  and  Allard,  H.  A. 

1922.  Photoperiodism,  the  response  of  the  plant  to  relative  length  of  day 

and  night.     Science,  n.s.,  vol.  55,  pp.  582-583. 
Gleason,  H.  A. 

1919.     Variability  in  flower  number  in  Vernonia  mussurica  Eaf.     Am.  Natur- 
alist, vol.  53,  pp.  526-534. 
Goodspeed,  T.  H.  and  Clausen,  R.  E. 

1915.     Factors  influencing  flower  size  in  Nicotiana  with   special  reference 
to  questions  of  inheritance.     Am.  Jour.  Bot.,  vol.  2,  pp.  332-374. 
Goodspeed,  T.  H.  and  Clausen,  R.  E. 

1918.     An    apparatus    for    flower    measurement.      Univ.    Calif.    Publ.    Bot., 
vol.  5,  pp.  435-438. 
Hayes,  H.  K. 

1912.     Correlation  and  inheritance  in  Nicotiana  tabacum.     Conn.  Agr.  Exp. 
Sta.  Bull.  No.  171. 
Juel,  H.  O. 

1905.     Die    Tetradteilungen    bei    Taraxacum    und    anderen    Cichorieen.      K. 
Svenska  Vetenskapsakad.     Handl.,  Bd.  39,  no.  4,  pp.  1-21. 
Klebs,  George 

1918.     tiber   die    Blutenbildung   von   Sempervivum.     Jena.    Festschrift    zum 
Ernst  Stahl,  pp.  128-151.     (Abstract  in  Bot.  Gaz.,  vol.  67,  p.  445.) 
Rosenberg,  O. 

1909.     Zur    Kentniss    von    den    Tetradteilungen    der    Compositen.      Svensk 
Botanisk  Tidskrift,  Bd.  3,  pp.  64-77. 
Rosenberg,  O. 

1918.     Chromosomenzahlen    und    chromosomendimensionen    in    der    Gattung 
Crepis.     Arkiv  for  Botanik,  Bd.  15,  no.  11,  pp.  1-16. 
Schmidt,  Jos. 

1918.     Investigations  on  Hops:     XL     Can  different  clones  be  characterized 
by  the  number  of  marginal  teeth  in  leaves'?     C.  R.  des  Travaux 
de  Laboratoire  de  Carlsberg,  Kj0benhavn,  vol.  14,  pp.  1-22. 
Shull,  G.  H. 

1914.     Duplicate  genes  for  capsule  form  in  Bursa  bursa-pastoris.  Ztschr.  induk- 
tive  Abstamm.  u.  Vererbungslehre,  vol.  12,  pp.  97-149. 
Shull,  G.  H. 

1918.     Duplication    of    leaf-lobe    factor    in    the    Shepherd's    Purse.      Mem. 
Brooklyn  Bot.  Garden,  vol.  1,  pp.  427-443. 
de  Smet,  Edmond 

1914.     Chromosomes,  prochromosomes,  et  nucleole  dans  quelques  dicotylees. 
La  Cellule,  vol.  29,  pp.  335-377. 
Stout,  A.  B.  and  Boas,  Helene  M. 

1918.  Statistical  studies  of  flower  number  per  head  in  Cichorium  intybus: 
kinds  of  variability,  heredity,  and  effects  of  selection.  Mem. 
Torrey  Bot.  Club,  vol.  17,  pp.  334-458. 


PLATE   42 

Fig.  1.     Very  young   stage;    cotyledons   still   persist. 

Fig.  2.     Early  rosette  stage. 

Fig.  3.     Later  rosette  stage. 

Fig.  4.  Nearly  mature  resette  in  a  family  showing  a  characteristic  retrorse 
rolling  of  the  leaf  margins. 

Fig.  5.  Fully  developed  rosette,  the  stage  in  which  measurements  of  length 
of  radical  leaves  were  taken. 


[240] 


UNIV.    CALIF.    PUBL.    AGRI.    SCI.    VOL.    2 


[  RAU  ]    PLATE  42 


¥ 


Fig.    1 


Fig.  2 


Fig.   3 


Fig.  4 


Fig.    5 


PLATE  43 

Fig.  1.  Fully  developed  plant  of  spreading  habit,  i.e.,  having  many  divari- 
cate branches  arising  from  the  base  of  the  axis.     Fully  open  capitula  shown. 

Fig.  2.  Nearly  mature  plant  similar  to  that  shown  in  fig.  1,  but  of  erect 
habit. 

Fig.  3.  Mature  plant  of  distinct  habit,  having  no  secondary  branches  arising 
from  the  base  of  the  axis. 

Fig.  4.     Mature  plant  of  spreading  habit,  but  a  dwarf  in  stature. 

Fig.  5.  Fully  open  capitula  such  as  were  used  in  taking  measurements 
of  diameter. 


[242J 


UNIV,    CALIF,    PUBL.    AGRI.    SCI.    VOL.    2 


[ RAU  |    PLATE   43 


Fig.    1 


Pig.  3 


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: 


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if  tJ 


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Fig.   4 


